Mammography and the Overdiagnosis of Breast Cancer
By Alan Cassels, Evidencenetwork.ca
VICTORIA, BC, Nov. 24, 2011/ - A few years ago two friends asked me if I’d like to “Run for the Cure” in support of the Canadian Breast Cancer Foundation. They had both been through bouts with breast cancer and so invited me to do the run. I agreed, only reluctantly.
Don’t get me wrong. I like running. And I like the fact that people are motivated to support better research for a disease that kills about 5,000 Canadian women every year. I even admit that jogging with a large group of determined, energized people wearing pink has lots of fun buzz and energy. At the same time since my work immerses me in the world of evidence-based medicine, and highlights the raging controversies that consume many areas of medical practice, I had reservations.
Misleading evidence about mammography
Besides the sticky problem of corporate influence over breast cancer research, and the annual pinkification of society that invokes the gag reflex in many of us, the enthusiastic survivors who say they owe their lives to mammography have probably been misled. And they are at risk of misleading other people about the value of breast cancer screening.
Mammography screening uses x-rays to find tumours in the breasts and is recommended for women between ages 50 and 74 in Canada, though even that recommendation is fiercely debated. Canada has had breast cancer screening programs in place for decades, but what we’ve never had is good evidence that annual mammograms are actually saving lives.
But evidence has been accumulating, and the picture is changing from one where mammography screening was believed to be saving many lives to one where one or two lives per thousand women screened are believed to be saved by screening.
An article in this week’s Canadian Medical Association Journal put forth the strongest argument against mammography screening ever seen in the pages of a prominent medical journal. In the commentary, Dr. Peter Gotzsche, a Danish researcher and a member of the internationally-acclaimed Cochrane Collaboration, said what some will find impossible to believe: “the best method we have to reduce the risk of breast cancer is to stop the screening program.”
His research highlights the key problem with breast cancer screening: overdiagnosis. Sometimes with screening, often what looks like a deadly cancer isn’t. Slight lesions in milk ducts in a woman’s breasts may look like cancer – and finding them on a mammogram inevitably starts the cascade of anxiety, biopsies, surgery, radiotherapy and drugs – even if the lesions would never have gone on to hurt the woman. And perhaps the most provocative thing of all: many breast cancer tumours just disappear on their own.
Dr. Gotzsche points to evidence that has been growing for years but is now nearly irrefutable, saying that “compelling data from the U.S., Norway and Sweden show that most overdiagnosed tumours would have regressed spontaneously without treatment.”
Women who feel something unusual in their breast should definitely get to a doctor and get it checked out. But if you are otherwise healthy, you should know going in for that mammography could mean you’ll get treatment you don’t need because mammography can’t tell us who needs treatment and who doesn’t.
As a world authority on the hard science behind breast cancer screening, Dr. Gotzsche has long studied the limitations of screening and he writes that the “level of over-diagnosis is about 50 per cent in those countries who have organized screening programs.” He adds: “If screening had been a drug, it would have been withdrawn from the market.”
What he says will be taken as incredibly controversial. People will pelt him with verbal rotten fruit (and they’ll save some for me for even reporting on his research), but I think his message must stand: Medicine must think about the safety of women being screened, and work to reduce the unnecessary harms that could come their way if they choose to participate in screening.
Might be blasphemy, but . . .
Stopping screening sounds like blasphemy to the thousands of women around the world who believe their lives were saved by it. The women who survive breast cancer and who become motivated, engaged, and public-spirited foot-soldiers in the war on breast cancer, shouldn’t stop their activism – they should be part of a new conversation. And that conversation should start here in Canada.
It’s not surprising that a Canadian medical journal has published such a provocative commentary, being that Canada has produced some of the best breast cancer screening research in the world.
The article ends with a challenge wrapped up in provocative question: “Which country will be first to stop mammography screening?” It is a gauntlet tossed our way, begging Canadians to start that much needed conversation.
Alan Cassels is an expert advisor with EvidenceNetwork.ca. He is also drug policy researcher at the University of Victoria and the author of Selling Sickness. His next book, Seeking Sickness, is on the medical screening industry. EvidenceNetwork.ca is a comprehensive and non-partisan online resource designed to help journalists covering health policy issues in Canada.
Source: Troy Media